I think any guest character that shares a likeness with a real-life person would be a HORRIBLE choice. It would ruin so much, Any sports star, Rambo, Terminator, Ash, etc...no thanks. A little too morbid for me to be sawing and cutting up and mutilating "real life" people.

Those like Freddy, Jason, Predator, Beetlejuice, Sam, Terminator Endoskeleton, etc work perfectly because there is no true likeness involved.

Bo' Rai Cho from "Mortal Kombat: Deadly Alliance" or Hotaru from "Mortal Kombat: Deception" would be pretty cool

Remember Mokap form Deadly Alliance? he was literally Carlos Pesina, who does all of the motion capture for MK.

I will only accept these two:

BloodRayne

Ivy from Soul Calibur